President Barack Obama's sinking approval numbers are hurting the re-election chances of Democratic Sen. Mark Udall in Colorado, where a new poll shows him in an ever-tougher fight in the swing state, The Hill reported Friday.

Citing results from a Democratic survey firm Public Policy Polling, Udall leads former GOP Senate nominee and tea party Republican Ken Buck by 46 percent to 42 percent, a closer result than in earlier polls of the race, The Hill reported.

Udall’s approval rating is in negative territory as well, with 41 percent disapproving and 40 percent approving, the poll showed.

Obama's approval rating is down to 43 percent compared with his 48 percent approval in a PPP poll in April, The Hill reported. Obama won the state with 51 percent of the vote in 2012.

It had been thought Udall would have little trouble with his re-election bid, but the PPP survey as well as an earlier Quinnipiac poll shows the race is much tighter than expected.

Buck lost to Sen. Michael Bennet (D-Colo.) in 2010 after making a series of gaffes on social issues, but holds a big lead in the primary, according to the PPP survey.

President Barack Obama's sinking approval numbers are hurting the re-election chances of Democratic Sen. Mark Udall in Colorado, where a new poll shows him in an ever-tougher fight in the swing state, The Hill reported Thursday.